This mixed-method comparative study examined lesson study in Japan as the original model, and interpretation and adaption of lesson study as an emerging new model of teacher professional development in Florida, the United States. The study found that lesson study has been interpreted through the lens of organizational structures and routines of teacher professional development in Florida and the U.S. in general, and the model was adapted to fit into the existing organizational contexts. The chapter discusses the underlying views of teacher professional development and the teaching profession in the U.S. that played an important role in the adaptation process of lesson study.